The goal of this project is to define methodologies by which to investigate the mechanisms of hair follicle growth and differentiation at the molecular level. The initial approach will focus upon follicle-specific protein gene expression in the mouse. This model system is uniquely advantageous as it offers a wide variety of relevant mutants of defined genetic background. The current project will involve preparation of molecular probes which, in subsequent projects, will be used to examine follicular regulatory mechanisms. Recombinant DNA technology will be used to prepare cloned complementary DNA probes with specificities for major hair keratin mRNAs. These probes will be characterized by positive hybridization selection translation assays to determine individual keratin specificities and appropriate specific fragments will be subcloned. Further characterization will be achieved by restriction mapping and nucleotide sequence analyses. Optimal conditions for in situ hybridization analyses using these probes directly in tissue sections will be determined. In this way, a technique will be developed by which to assess qualitative and semi-quantitative distributions of hair follicle keratin mRNAs. Through these studies a foundation will be established upon which the longer-term objective of understanding corresponding pathological processes of hair follicles may be reached.